COT (Constant On-Time) control has been widely used with DC/DC voltage converters for its fast transient response. However, the switching frequency of the COT controlled voltage converter is variable and not constant, which makes COT control hardly applied in cases where a constant switching frequency is essentially required, such as an automobile system. Contrarily, peak current mode control has a constant switching frequency, but it is slow in transient response, and the minimum on time of a power switch during each switching cycle is required to implement current sensing function.
Consequently, a control circuit and scheme thereof with fast transient response and constant switching frequency is needed.